DE2306752B1 - DEVICE FOR THE CAPACITIVE SCANNING OF CIRCULAR AND LENGTH DIVISIONS - Google Patents

Description

and the line grid 8 is electrically conductively connected to a connection 10 on the fixed part 2. the Shield 3 is on the movable part 1 with a connector 11 and the shield 6 on the fixed part 2 connected to a terminal 12 in an electrically conductive manner.

The length dividing device shown in FIG. 2 consists like the circle dividing device according to FIG. 1 made of two glass bodies with vapor-deposited thin-film layers. A movable part 13 is arranged at a fixed distance A - precisely positioned over a fixed part 14 and freely displaceable in the longitudinal direction.

On the movable part 13 are vapor deposited: a shield 15, electrically connected with a connection 16, an insulation 17

and a line grid 18, electrically conductively connected to a connection 19. The following are vapor-deposited on the fixed part 14:

a shield 20, electrically conductively connected to a terminal 21, an isolation 22

and a line grid 23, electrically conductively connected to a terminal 24. The lines of the movable line grid 5 and the fixed line grid 8 (FIG. 1) and of the movable line grid 18 and the fixed line grid 23 (FIG. 2) form small plate capacitors with constant plate spacing A, but with a variable coverage area.

The capacitance values that can be measured at the electrical connections 9 and 10 or 19 and 24 are dependent of the relative position of the movable line grids 5 or 18 to the fixed line grids 8 or 23. The shields 3 and 6 or 15 and 20 with their electrical connections 11 and 12 or 16 and 21, which are connected to earth potential, together with the one to be described below, have the effect Type of wiring a strong reduction of the stray capacities. This increases the sensitivity of the Arrangement compared to known capacitive scanning methods much improved.

The sensitivity is defined as the ratio the maximum capacity (if the line grid lines of the movable line grid 5 or 18 and the fixed line grid 8 or 23 cover) to the minimum capacity (if the line grid lines of the movable line grid 5 or 18 by half a grid position relative to the lines of the fixed line grid 8 and 23 are shifted). So that the constant capacities between the Line grids 5 or 18 or 8 or 23 and the shields 3 or 15 or 6 or 20 are small, the If the stray capacitances are shielded as effectively as possible, the shields are made in the form of a line grid formed with the same grid division as the line grids 5 or 18 and 8 or 23. The shields but can also be designed as continuous thin metal layers. Correspondingly larger constant capacities are required be accepted.

Another possibility for the design of the shield is to use it as a line grid reduced line width on the same level as the line grid. The lines of the shield in this case come to lie between the lines of the line grid. The one through the reduced The space created by the line width acts as insulation.

In Fig. 4 and 5 all partial capacities are shown, those between a line of the movable line grid 5 or 18 of the shield 3 or 15 and the fixed line grid 8 or 23 and the shield 6 or 20 exist; F i g. 5 shows the movable one Part 1 or 13 compared to the position in FIG. 4 shifted by half a division.

Fig. 4 shows the partial capacities with the lines of the two line grids in the intermediate position: It denotes

C _{1 is} the capacitance between a line of the line grid 5 or 18 and the earthed shield 3 or 15; C ₁ is independent of the rotary movement or the displacement;

C _{2 is} the capacitance between a line of the line grid 5 or 18 and the shield 6 or 20; C ₂ is a function of the rotational movement or the displacement;

C _{3 is} the capacitance between a line of the line grid 5 or 18 and the neighboring lines of the line grid 8 or 23; C ₃ is a function of rotational movement or displacement;

C ₄ the capacitance between two adjacent lines of the line grid 8 or 23 and the shield 6 or 20; C ₄ is independent of the rotary movement or of the displacement;

C _{5 is} the capacitance between the lines of the fixed line grid 8 or 23 and the earthed shield 3 or 15 on the rotatable or displaceable part 1 or 13; C ₅ is a function of rotation or displacement;

Fig. 5 shows the partial capacities with the lines of the two line grids in overlapping position:

C ₁ and C ₄ have not changed due to the relative shift and are still present;

C _{6 is} the capacitance between a line of the movable line grid 5 or 18 and the opposite line of the fixed line grid 8 or 23; C ₆ is a function of the rotary movement or the displacement.

As a result of the relative shift by half a grid division, the partial capacities - as shown in FIG. 4 shows - from C ₁ , C ₂ , C ₃ , C ₄ and C ₅ to C ₁ , C ₄ and C ₆ - like FIG. 5 shows - changed.

In Fig. 6 the partial capacities are summarized as:

a) the line capacitance C ₇ ; it is composed of the partial capacities that are present between the lines of the line grids;

b) the shielding capacitance C _{8 of} the rotatable or displaceable part 1 or 13; it is composed of the partial capacitances between the lines of the line grid 5 or 18 and the earthed shielding 3 or 15 and 6 or 20;

c) the shielding capacitance C _{9 of} the fixed part 2 or 14; it is composed of the partial capacitances between the lines of the line grid 8, 23 and the earthed shields 6 or 20 and 3 or 15.

The shielding capacitance C ₈ is, as in FIG. 6 shows, at connection 11 or 16 via the bearing, the

shielding capacitance C ₉ at connection 12 or 21 switched to ground potential.

The connections 11 or 16 and 12 or 21 are therefore to be considered as a single connection, there both are switched to earth potential.

_{The capacities C 7} , C ₈ and C ₉ in FIG. 6 combined from partial capacities are a function of the rotary movement or the displacement.

With the lines of the line grid in the relative position (as Fig. 4 shows):

C ₇ = C ₃

O ₈ -O ₁ -TO ₂

With the lines of the line grid in the relative position (as Fig. 5 shows):

is connected, which supplies a current I ₁ independent of the load and with an ammeter 30 or with a current-amplitude-sensitive circuit at the fixed contact 25, the output current / _{0 is} measured.

The internal resistance of the ammeter 30 is very small. This means that C ₉ can be neglected. The equivalent circuit is simplified as a result, as FIG. 10 shows. In general, the following applies to the output current:

j -! C ₇ ^{u 1} C ₊ C

With the lines in the relative position, as shown in FIG. 4 shows, the output current Z ₀₁ at the fixed contact 25 is expressed with partial capacitances:

7 shows a complete electrical equivalent circuit the arrangement shown in FIG. 6, with a voltage generator on a fixed contact 25 26 and on a sliding contact 27 a voltmeter 28 or a voltage amplitude sensitive measuring circuit connected.

The voltage generator 26 supplies a voltage F ₁ independent of the load at the fixed contact 25. The combined capacitance C ₉ can thus be omitted: the equivalent circuit is simplified and the capacitances C ₇ and C ₈ remain, as shown in FIG. 8 shows. The two capacitances C ₇ and C ₈ are a function of the rotary movement or the displacement.

In general, the output voltage F ₀ at the sliding contact 27

Vv = V ₁ -

C ₇

With the lines of the line grids 5 or 18 and 8 or 23 in the relative position, as shown in FIG. 4, the output voltage F ₀₁ at the sliding contact 27 is expressed in partial capacities:

V = V C ₃

^{01 1} C ₊ C ₊ C

With the lines in the relative position (as _{Fig. 5 shows), the output voltage F 02} at the sliding contact 27 is expressed with partial capacitances:

V = V ^C

' ft') Γ 1

CA-C
O ₆ -I- O ₁

By shifting the line grids 5 or 18 and 8 or 23 relative to half a division (as shown in FIGS. 4 and 5), the output voltage at the sliding contact 27 changes from F ₀₁ to F ₀₂ . The ratio of the two output voltages F ₀₁ and F ₀₂ ii Mß fü di Efidlihki d
order:

gpg ₀₁

₀₂ is a measure of the sensitivity of the And

Sensitivity = - ?? - = -

V ₀₁

C ₃ ArC ₁ + C ₂

The same sensitivity result is obtained if - like the complete equivalent circuit in FIG. 9 shows - a power generator 29 on sliding contact 27

^{01 1}

C ₁

With the lines in the relative position, as shown in Fig. 5, the output current J ₀₂ at the fixed contact 25 is expressed with partial capacitances:

• * 02 * ■■

o ₆ τ O ₁

The ratio of the output currents Z ₀₁ , Z ₀₂ is again the measure of the sensitivity of the arrangement.

Sensitivity = ^ - = ■

St.

CA-CA-C

The mode of operation of the incremental capacitive scanning of circular and length divisions should now with reference to FIGS. 1 to 6 and the electrical equivalent circuits Fi g. 7 to 10:

The size to be measured is with the movable part 1 for angle measurements and the part 14 for Length measurements coupled. In the case of the division of a circle (FIG. 1), the rotatable part 1 is designed as a disk and allows angle measurements over 360 degrees. The fixed part is a sector of any arc length educated.

In the longitudinal division of FIG. 2, the movable part 13 is designed as a section of any length. The fixed part 14 extends as a scale over the entire length to be measured.

The lines of the line grid 5 or 18 on the movable part 1 or 13 together with the lines of the line grid 8 or 23 on the fixed part 2 or 14 form small plate capacitors with the fixed plate spacing A, but with a variable plate coverage area.

By rotating the movable part 1 or shifting the movable part 13 relative to the fixed part 2 or 14 changes the coverage area of the lines.

From Fig. 1 and 2 it can also be seen that all Lines of the line grid 5 or 18 or 8 or 23 electrically connected and connected to the electrical Connections 9 or 19 and 10 or 24 are performed.

The capacitance that can be measured between the electrical connections 9 or 19 and 10 or 24 is the sum of all line capacities between the line grid 5 or 18 and 8 or 23. The capacity becomes a minimum with the line grids 5 or 18 and 8 or 23

in relative position according to FIG. 4 and a maximum with the line grid 5 or 18 and 8 or 23 in relative position according to FIG. 5.

The capacitance that can be measured between the electrical connections 9 or 19 and 10 or 24 changes with the relative displacement of the line grids 5 or 18 or 8 or 23 within a grid division from Minimum value to the maximum value (can be seen from FIGS. 4 and 5). The number of times during a rotation or displacement traversed minimum values or maximum values of the capacity is the same the number of raster divisions run through. Multiply the number of raster divisions run through with the grid division constant (an angle increment for circular divisions and a Length increment), one obtains the size of the angle of rotation or the measure of the length of the Shift.

The smaller the grid division and thus the grid division constant can be held, the greater the resolution of the scanning process.

Since the capacitance of the line capacitor 5, 8 or 18, 23 is proportional to within a grid division Relative position of the grid leads to a measurement of the capacitance relative to the maximum or minimum value to further improve the resolution.

In the practical case, the capacitance is not measured directly, but the output signal, which is amplitude-modulated by the change in capacitance, is evaluated. A low-resistance generator 26 with a fixed frequency is connected to the contact 25 (FIGS. 6, 7, 8). The generator supplies the load-independent input voltage V ₁ ; C ₉ can therefore be neglected.

The output voltage V ₀ in the simplified equivalent circuit (FIG. 8) is measured at the sliding contact 27 with an amplitude-sensitive measuring circuit 28 with a high input impedance. The capacitances C ₇ and C ₈ represent a capacitive voltage divider. C ₇ and C ₈ are dependent on the relative position of the line grids 5 or 18 and 8 or 23 and consist of line capacities of the line grids 5 or 18 and 8 or 23 as well of the shields 3 resp.

15 and 6 or 20.

The amplitude of the output voltage is proportional to the relative position of the lines in the line grid 5 or 18 and 8 or 23 within a grid division, and the number of maxima and minima is equal to the number of raster divisions passed through. By counting the minimum or maximum values

* 5 as well as measuring the amplitude of the output voltage V ₁ by means of known electronic circuits, the amount of the measured variable (angle or length) can be displayed digitally.
The same applies to that shown in FIGS

ao circuit type:

The constant current I _{1 is} fed in at the sliding contact 27 with the high-resistance generator 29 of a fixed frequency. The output current / ₀ is measured at the sliding contact with the low-resistance current amplitude-sensitive measuring circuit 30. The low-resistance measuring circuit 30 is parallel to C ₉ , which means that C ₉ can be neglected. _{The two capacitances C 7} and C _{8 which are} dependent on the relative position of the line grids 5 or 18 and 8 or 23 and the shielding 3 or 15 and 6 or 20 remain. By measuring the amplitude and counting the number of maximum or minimum values of the output current I ₀ , the amount of the measured variable is again obtained as an angle or length, as in the circuit type shown in FIGS.

For this purpose 2 sheets of drawings

409513/270

Claims (8)

1 2 ken as a thin metal layer on a glass substrate on Patent claims: vaporized; a line grid created in this way is moved with a second grid compared to the first 1. Device for capacitive scanning of borrowed raster scanned. Shift the dash-circle and length divisions, in which on a 5 grid against each other, then result electrically measurable and on a moving part a bare and within certain limits the electrical shift Conductive grid of lines is arranged, exercise proportional changes in capacitance, the pre-thereby characterized that on the preferably with electronic methods to increfesten Part (2; 14) and / or the movable mental measurement of angles and lengths out-part (1; 13) one of the two line grids can be evaluated. (5, 8; 18, 23) electrically isolated, correct electrical potential switched elec- trically conductive layer (3, 6; 15, 20) arranged ßer stray capacitances low and thus for extremely is through which at least the gaps between precise circular and length measurements - as z. B. see the lines of the associated line grid 15 are required in the measuring device construction - insufficient. (5, 8; 18, 23) are shielded from the outside. The object of the invention is the sensitivity 2. Apparatus according to claim 1, characterized in that such capacitive scans are essentially that the one line grid (8 or better and thus the accuracy especially in 23) to a voltage source (25) connected measuring devices to increase significantly. is and the output voltage of the other line 20 According to the invention, this is achieved in that raster (5 or 18) of a stress amplitude on the fixed part and / or the movable part sensitive measuring circuit (28) is supplied. switched to a certain electrical potential, 3. Device according to claim 1, characterized in that one of the two line grids is electrically isolated, indicates that one line grid (8 or electrically conductive layer is arranged through which 23) connected to a power source (29) and 25 at least the spaces between the lines the output current of the other line grid (5 of the associated line grid is drawn to the outside or 18) a current-amplitude-sensitive screen. Measuring circuit (30) is supplied. The invention is described below with the aid of 4. Apparatus according to claim 1, characterized in that there are geometrical drawings of exemplary embodiments indicates that the shield (3, 6 or 30 explained with further details. It shows 15.20) between the line grid carrier (1, 2 or Fig. 1, a circle setting device with line 13,14) and line grids (5, 8 or 18, 23) rasterized and shielding, is arranged. Fig. 2 shows a length dividing device with 5. Apparatus according to claim 1, characterized by line grid and shielding, indicates that the shield (3, 6 or 35 F i g. 3 has a cross section along the lines ΠΙ-ΠΙ 15, 20) is also designed as a line grid. inFig. Iund2, 6. Apparatus according to claim 5, characterized in Fig. 4 is a circular or longitudinal section along the indicates that the shield is in the same line IV-IV in FIG. 1 and 2, Level like the associated one, the capacitive output F i g. 5 shows a similar circular or longitudinal section Bar grids (5, 8; 18, 23) in 40 as in FIG. 4, but with the relative position between them Interstices is arranged. see moving and fixed part opposite F i g. 4th 7. The device according to claim 2, characterized in that it is shifted by half a division,
6 shows a section through a circular or length alternating voltage generator (26) of constant frequency division device similar to FIG. 3, sequence is connected and the second line 45 Fig. 7 the electrical equivalent circuit of the circular grid for measuring the capacitance and length division device operated with spanning amplitude-modulated output signal with voltage generator, a voltage amplitude demodulation circuit. Fig. 8 shows a simplified electrical equivalent circuit (28) high input impedance is connected. tion of the circle and length division device, loading 8. The device according to claim 2, characterized by 5 ° driven with a voltage generator, indicates that one line grid on a Fig. 9 shows the electrical equivalent circuit of the circuit Current generator (29) of constant frequency and length division device operated with is closed and the second line grid to the power generator, Measurement of the amplification caused by the change in capacitance. Fig. 10 a simplified electrical equivalent circuit tuden-modulated output signal with a 55 tang of the circle and length division device, Current amplitude modulation circuit (30) operated small with a current generator. connected to an input impedance. The in F i g. 1 shown circle dividing device has two glass bodies, namely a movable part 1 and a fixed part 2; the movable one 60 Part 1 is at a fixed distance A on fixed part 2 precisely centered, freely rotatable. On the movable part 1 are a shield 3, a Isolation 4 and a grid of lines 5 in the above The invention relates to a device for the capacitive sequence - as also shown in FIG. 3 - in the thin citizen Scanning of circular and length divisions, 65 vapor-deposited film process. Likewise are on the in the case of the part 2 fixed on a fixed and a movable part, a shield 6, an insulation 7 an electrically conductive grid of lines is arranged in each case. and a line grid 8 is vapor-deposited. The line grid 5 The line grid is usually with line mesh with a connection 9 on the movable part 1